N4448LCessna 172G · 1966

On May 16, 2024, about 0900 Pacific daylight time, a Cessna 172G airplane, N4448L, was substantially damaged when it was involved in an accident near Lakeport, California. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that he was flying locally and conducting full-stop landings at Lampson Field Airport (1O2), Lakeport, California. After performing three takeoffs and landings, he taxied back to his hangar and then decided to perform one more flight in the traffic pattern. The pilot taxied back to the run-up area and performed a run-up before departure, which included a magneto check and activation of the carburetor heat, both of which resulted in an rpm drop.

On the accident flight, the airplane reached rotation speed and lifted off normally. As the airplane started to climb, the engine lost power, and the airplane stopped climbing. The pilot stated that he was too low to turn back to the runway and decided to continue straight and initiated a forced landing to an open field. During the landing sequence, the empennage impacted a barbed wire fence and separated from the fuselage.

The nearest weather reporting station, Ukiah Municipal Airport (UKI), Ukiah, California, was 16 nautical miles northwest of the accident site. At 0856, the reported temperature was 55.4°F with a dewpoint of 50°F. The calculated relative humidity at this temperature and dewpoint was about 82%.

FAA Special Airworthiness Information Bulletin (SAIB) CE-09-35, Carburetor Icing Prevention, indicated that the atmospheric conditions at the time of the accident were conducive to serious icing at cruise power. Furthermore, the SAIB states that pilots should be aware that carburetor icing doesn't just occur in freezing conditions but can also occur at temperatures well above freezing temperatures when there is visible moisture or high humidity. Vaporization of fuel, combined with the expansion of air as it flows through the carburetor (Venturi Effect), causes sudden cooling, sometimes by a significant amount within a fraction of a second.

Additionally, FAA Advisory Circular (AC) 20-113 states, "To prevent accidents due to induction system icing, the pilot should regularly use [carburetor] heat under conditions known to be conducive to atmospheric icing…" The AC also recommends that when operating in conditions where the relative humidity is greater than 50% and the temperature is below 70°F, a pilot should briefly apply carburetor heat immediately before takeoff to remove any ice that may have been accumulated during taxi and runup, and remain alert for indications of induction system icing during takeoff and climb-out, especially when the relative humidity is above 50%, or when visible moisture is present in the atmosphere. According to SAIB CE-09-35, carburetor ice can be detected by a drop in rpm in fixed pitch propeller airplanes and a drop in manifold pressure in constant speed propeller airplanes.

The postaccident examination of the engine revealed no obvious holes in the crankcase. The fuel system was examined with no breaches noted, and continuity of the fuel system was confirmed from the wings to the carburetor. Each cylinder was borescoped and did not reveal any evidence of a mechanical failure of the pistons or valves. The spark plugs showed normal wear according to the Champion Aviation Check-A-Plug Chart AV-27; however, the No. 5 bottom spark plug was carbon/oil fouled. The engine started and was run for about 3 minutes at idle rpm. Due to the damaged propeller blades, a full run-up was not performed. A functional check of the magnetos and carburetor heat showed a normal rpm drop, and the power loss could not be replicated. The postaccident examination of the airframe and engine revealed no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.